Maintaining a consistent air gap between the rotor and stator in electromechanical machines such as permanent magnet motors and generators is a critical aspect of efficient operation. On small diameter conventional motors and generators it is not difficult to design a machine structure that can maintain air gap clearance using conventional design methods. Maintaining a consistent air gap becomes more difficult for high torque, low speed machine designs, such as for the design of direct drive, gearless wind turbines, where the generator rotational speed is dictated by the wind turbine aerodynamic rotor. As one illustrative example, in a multi-MW class wind turbine the generator for a direct drive configuration may be required to produce its rated output power and torque at speeds in a general range of 14-16 rpm. A generator or motor in this general power and speed range must have a large air gap diameter, typically in the range of 3-5 meters. At these sizes under the experienced loads for such turbines, it becomes a design challenge to build a generator structure stiff enough to maintain the air gap integrity under all load conditions while maintaining the weight of the structural elements at a reasonable level.
Attempts have been made to add various bearing structures in order to address this problem. However, such proposed solutions generally involve relatively conventional bearing structures located at or close to the air gap to stabilize the air gap. But these conventional bearing-type solutions involve continuous load bearing structures with continuous contact that increase the weight and complexity of the design and add an additional maintenance item to the turbine design. As such, conventional solutions to this problem to date have been less than satisfactory.